There is a substantial and growing interest in the development and use of electric vehicles to alleviate the world's pollution problems and reduce the use of nonrenewable fossil fuels. The biggest problem in the development of such vehicles has been the inadequacy of conventional batteries to provide the energy required by such vehicles.
Zinc-air primary (non-rechargeable) cells and secondary (rechargeable) zinc-air cells have been disclosed which might meet some of the requirements of practical electric vehicles. Ross, U.S. Pat. No. 4,842,963 issued Jun. 27, 1989, describes a secondary zinc-air battery which recirculates electrolyte through porous foam electrode containing deposited zinc by means of an external pump and electrolyte reservoir.
Doniat, et al U.S. Pat. Nos. 3,887,400 issued Jun. 3, 1975, 3,981,747 issued Sep. 21, 1976, and U.S. Pat. No. 4,126,733 issued Nov. 21, 1978, provide another approach to rechargeable zinc-air cells. In these systems electrolyte is passed upwardly through a zinc particle bed. Various techniques for electrochemically regenerating the zinc in situ are also described.
Solomon, et al. U.S. Pat. No. 4,147,839 issued Apr. 3, 1979, describes a cell using a stirred metal powder and cell electrolyte slurry. While not requiring the use of a pump during discharge to transfer electrolyte to and from the cell, the battery still must draw energy during discharge in order to drive the cell's agitator which in this case is a pitched impeller used to stir the mixture.
A problem with currently available systems is that pumps are required to recirculate the electrolyte through external loops during discharge. Pumps consume a substantial amount of energy and add considerable weight to the battery. This makes the presently available zinc air cells poorly suited for electric vehicles as a large number of such cells are necessary to provide adequate power.
Savaskan and Evans, U.S. Pat. No. 5,006,424 issued Apr. 9, 1991 describes a cell which has demonstrated promising electrical performance. Besides its electrical performance, this cell is attractive because it is "hydraulically" recharged. The zinc is present as particles and recharging consists of the hydraulic removal of reacted particles and electrolyte at a service station. Replenishment could be accomplished in a matter of minutes in a manner similar to refueling procedures used with internal combustion engine vehicles.
The disadvantage to the use of hydraulically recharged cells in electric cars is that they require service stations to replenish the zinc particles and electrolytes in a market acceptable manner. The difficulty of establishing the infrastructure of such refueling stations makes the practical, broad application of hydraulically recharged cells less attractive.
For the above as well as other reasons the ability to electrically recharge, at home or in electrical recharging stations is important for the practical general use of electric cars. Because the present invention meets this challenge by being capable of both electric and hydraulic recharging, it represents a dramatic breakthrough in the development of electric vehicles. Zinc-air cells as described in this application would offer significant advantages over presently available batteries.